1. Field of the Invention
The present invention relates to an organic electro-luminescence device and a fabricating method thereof. More particularly, the present invention relates to an organic electro-luminescence device and a fabricating method thereof wherein a picture quality is improved and a luminous efficiency is increased.
2. Description of the Related Art
Recently, there have been developed various flat panel displays, reduced in weight and bulk, that are capable of eliminating the disadvantages of a Cathode Ray Tube (CRT). Such flat panel displays include a Liquid Crystal Display (hereinafter referred to as a “LCD”), a Field Emission Display (FED), a Plasma Display Panel (hereinafter referred to as a “PDP”) and an Electro-Luminescence (hereinafter referred to as an “EL”) display, etc. There is an ongoing effort to improve the image quality of a flat panel display, and an ongoing effort to manufacture flat panel displays of larger size.
At present, a PDP has many advantages. A PDP is light weight and thin. Further, the PDP can have a large size thanks to a simple configuration and fabrication process. On the other hand, a PDP has some disadvantages, such as a low luminous efficiency, low brightness and high power consumption.
In comparison with a PDP, an active matrix LCD, using a Thin Film Transistor (hereinafter referred to as a “TFT”) as a switching device, is difficult to manufacture in a large size. Also, an active matrix LCD has the disadvantage of high power consumption due to a back light unit, large optical losses owing to optical devices such as a polarizing filter, a prism sheet, a diffuser, etc., and a narrow viewing angle.
An EL device is classified into an inorganic EL device and an organic EL device according to the materials used in a light-emitting layer of the EL device. EL devices have the advantages of a fast response speed, a high luminous efficiency and brightness, and a wide viewing angle. As compared to the organic EL device, the inorganic EL device has higher power consumption, reduced brightness and does not emit various lights of R, G and B. On the other hand, the organic EL device has the advantages of lower driving voltage (e.g. reduced power consumption), a fast response speed, high brightness and light-emitting of various colors of R, G and B, such that it is suitable for a post-generation display device.
FIG. 1 is a sectional view of an EL layer of a conventional EL device, and FIG. 2 is a diagram illustrating a light-emitting principle of the conventional EL device.
The EL layer shown in FIG. 1 includes an organic light-emitting layer 10 formed between a first electrode (or an anode) 4 and a second electrode (or a cathode) 12. The organic light-emitting layer 10 includes an electron injection layer 10A, an electron carrier layer 10B, a light-emitting layer 10C, a hole carrier layer 10D and a hole injection layer 10E.
A predetermined voltage is applied between the first electrode 4 and the second electrode 12, as shown in FIG. 1. As illustrated in FIG. 2, the predetermined voltage causes electrons produced from the second electrode 12 to move, via the electron injection layer 10A and the electron carrier layer 10B, into the light-emitting layer 10C. Moreover, holes produced from the first electrode 4 move, via the hole injection layer 10E and the hole carrier layer 10D, into the light-emitting layer 10C. Thus, the electrons and the holes fed from the electron carrier layer 10B and the hole carrier layer 10D emit light upon their re-combination at the light-emitting layer 10C. The light is, emitted to the exterior via the first electrode 4 to thereby display a picture.
The hole injection layer 10E controls the concentration of holes. The hole carrier layer 10D controls the movement speed of the holes. By this arrangement, the holes produced from the first electrode 4 are easily injected into the light-emitting layer 10C.
The electron injection layer 10A controls the concentration of the electrons. The electron carrier layer 10B controls the movement speed of electrons. By this arrangement, the electrons produced from the second electrode 12 are easily injected into the light-emitting layer 10C.
The first electrode 4 is made from transparent and conductive substances such as an indium tin oxide (ITO), a tin oxide (TO) or an indium zinc oxide (IZO), or other similar substances. The first electrode 4 can be formed on a substrate and may also include Au, Pt, Cu and similar substances.
The hole injection layer 10E is formed by depositing mainly Copper (II) Phthalocyanine. In one embodiment, the hole injection layer is about 10˜30 nm thick.
The hole carrier layer 10D is formed by depositing mainly N,N-di(naphthalene-1-yl)-N,N′-diphenylbenzidine (NPD). In one embodiment, the hole carrier layer is about 30˜60 nm thick.
The light-emitting layer 10C mainly emits light by bringing-electrons and holes together. As occasion demands, the light-emitting layer 10C uses a light-emitting substance independently, or one doping on a host material.
In the case of emitting green (G) light, out of red (R), green (G) and blue (B) lights, the light-emitting layer 10C is formed by doping N-methylquinacridone (MQD) on the host material like tris(8-hydroxyquinolate)aluminum (Alq3). In one embodiment, the light-emitting layer is about 30˜60 nm thick. Moreover, in the case of using a light-emitting substance independently, the light-emitting layer 10C is formed by doping mainly Alq3 to emit the green light.
The electron carrier layer 10B is formed by depositing metal-complex compounds, like Alp3. In one embodiment, the electron carrier layer is about 20˜50 nm thick.
The electron injection layer 10A is formed by depositing alkali metallic derivatives. In one embodiment, the electron injection layer is about 30˜60 μm thick.
In the case of low molecules, the hole carrier layer 10D, the hole injection layer 10E, the light-emitting layer 10C, the electron carrier layer 10B, and the electron injection layer 10A are formed by a vacuum depositing method. In the case of high molecules, the hole carrier layer 10D, the hole injection layer 10E, the light-emitting layer 10C, the electron carrier layer 10B, and the electron injection layer 10A are formed by a spin coating method or an ink-jet printing method.
The second electrode 12 can be formed by using mainly Al, Li, Ca, Mg or Ba, having low work functions. Most commonly, the second electrode 12 is formed using metals like Al. A TFT array portion may be formed or positioned in lower part of the EL layer.
A drawback of an organic EL device, as described above, is that the organic EL device is easily deteriorated. To solve such a problem, a packaging plate 20 is attached to it. The packaging plate 20 encapsulates the organic EL device, as shown in FIG. 3.
The packaging plate 20 covers the EL layer formed on the substrate 2, and prevents the EL layer from being deteriorated by moisture and oxygen in the atmosphere. Further, the packaging plate 20 emits heat generated by the light-emission of the EL layer, and removes moisture and oxygen inside of the packaging plate 20 and the substrate 2 using an absorbing material, neutralizer or getter 16, formed on the back of the packaging plate 20. By this arrangement, the packaging plate 20 protects the EL layer 10 from moisture and oxygen in the atmosphere.
Despite the encapsulation process, the problem persists that the property of the EL layer is deteriorated. The deterioration occurs because small amounts of moisture and oxygen are not completely removed. The small amount of remaining moisture and oxygen, which is not removed during the encapsulation process, gathers or concentrates, between the second electrode 12 and the organic EL layer 10. Specifically, the oxygen and the moisture gathers or concentrates in the area where the organic EL layer 10, as an organic material, and the second electrode 12, as a metal, contact each other. The two materials have abrupt differences in surface energy, as a result Al203 is formed by a reaction of the metallic substance of the second electrode 12, like Al and O2.
The deterioration or oxide layer between the second electron 12 and the organic layer 10 restricts movement of electrons produced by the second electrode 12. Hence, the efficiency of the recombination of the holes and electrons in the light-emitting layer 10C is deteriorated. As a result, there arises a problem that a picture quality is deteriorated, due to a blurring effect, as illustrated in FIG. 4.